Description: (Applicant's Description) The Mouse Genetics Facility makes available embryonal stem cell ("knockout") technology and transgenic mouse technology to generate mutant mice to study gene function and regulation and to serve as models of disease. The mutant mice are engineered via gene targeting in embryonic stem (ES) cells and injection of ES cells into blastocysts, and via injection of DNA into pronuclei of fertilized oocytes. Additional embryo manipulation procedures are also performed regularly, e.g., collection of preimplantation stage embryos, inner cell mass (ICM) isolation by immunosurgery, embryo cryopreservation, morula aggregation, and electrofusion of two-cell embryos followed by aggregation of the resulting tetraploid embryos with ES cells or diploid morulae. A variety of molecular biology and tissue culture procedures are also offered: Southern blot and PCR genotyping of ES cell and mice (mouse tail) DNA and establishment of ES cells from mutant mouse lines.